The present invention relates to an automatic cleaning process, carried out during cleaning sequences during which all or at least part of an element to be cleaned, such as a spraying robot, is cleaned. Each element to be cleaned is positioned inside a booth with a controlled atmosphere belonging to a coating facility, such as an automotive paint facility. In a known manner, a painting booth comprises a conveyor to move the parts to be painted, such as automotive vehicle bodies, and one or several spraying robots of the multiaxial type, which are positioned on the side of the conveyor. The spraying robot(s) are supported by a grating or suspended from a vertical structure.
Generally, the air in a painting booth is regulated in terms of temperature and hygrometry to ensure good application of the paint on the surface to be painted. This dual regulation requires treatment of the outside air involving successive cooling and heating steps of the air to bring the air to a certain temperature and a certain humidity level. This air treatment creates high energy consumption and CO2 discharge into the atmosphere.
To resolve this drawback and thus comply with the environmental standards applicable to automobile manufacturing plants, it is known to recycle the air from the booth. In practice, ventilation of a modern booth operates with 90 to 100% recycled air.
The average transfer rate for application of the coating product is comprised between 70% and 80%: part of the sprayed paint is therefore not deposited on the surface to be painted. This lost paint is commonly called “overspray” in the coating field.
Part of the overspray can be recovered in a filtration system positioned in the lower part of the booth, below the grating. To that end, a ventilation system is used to generate a vertical stream of air directed from top to bottom, which makes it possible to guide the drops of paint toward the filtration system. Typically, the filtration system comprises a washer having a water reserve in the case of a traditional washer or a powder reserve in the case of a dry washer. This water or powder reserve is intended to absorb the drops of paint from the overspray. The filtration system therefore makes it possible to separate the air and the drops of paint, and to reuse the air for ventilation.
The other part of the overspray is deposited on the equipment installed in the booth, such as the sprayers and the robots, and optionally on the walls of the booth itself. The drops of paint deposited on the equipment thus risk building up and, over time, falling on the surface to be painted. Finishing defects may then appear on the bodies. Such defects require a partial or total touchup of the coated surface.
Thus, the equipment in the booth must be cleaned periodically. In practice, production stoppages are arranged to that end with a frequency of 2 to 4 hours for coating the inner parts of the body and frequency of 4 to 8 hours for coating the outer parts. During production stoppages, the operators enter the inside of the booth with cloths imbibed with solvent and manually clean the booth equipment. However, these operations are costly in terms of personnel. Furthermore, if the air in the booth is recycled, it nevertheless remains polluted with volatile organic compounds (VOC), such as solvent vapors, which are harmful to operators' health. The operators must therefore protect themselves with specific equipment, which is cumbersome and hinders their mobility.
To offset these drawbacks, some booths comprise an automatic cleaning system, comprising a rinsing box. This automatic cleaning system operates each time there is a change of the vehicle in the work zone of the robot and/or upon each change of color. The multiaxial robots bearing sprayers are then moved inside the rinsing box installed on the edge of the booth and are cleaned by applying a liquid solvent. The robots are next dried by one or several air jets. The rinsing box therefore also serves as a drying box. This limits the space occupied inside the booth, but does not allow effective drying of the solvent applied on the surfaces of the sprayer.
In practice, the time needed to change colors and the time to change vehicles in the coating product application zone, which depends on the production rhythm, are very short, such that the time allocated for cleaning is also very short, around 10 seconds, which does not allow in-depth cleaning of the outer surfaces of the painting equipment. Indeed, a large portion of this period is dedicated to drying, in order to avoid polluting the surfaces of the body with solvent. Thus, the current cleaning systems are only designed to clean the end of the head of the sprayer. This is for example the case for the systems described in WO-A-97/18903 and WO-A-2015/169432.
Thus, the other parts of the sprayer, such as the cover or the body on which the skirt is fastened, are not cleaned. Furthermore, certain parts of the robot itself, such as the handle, are not cleaned. These uncleaned parts therefore remain stained with coating product, which may drip on the surface to be painted during the application of the product and thereby create finishing defects.
Some rinsing boxes have nozzles that are movable along an axis, which makes it possible to rinse a larger surface area and reduce the number of injectors.
Furthermore, other solutions have been implemented to increase the time allocated cleaning. One solution consists of positioning the rinsing box as close as possible to the position of the robot at the end of application of the product. Another solution consists of using a set of two sprayers. While the first sprayer is working, the other sprayer is cleaned. One then has a longer period dedicated to cleaning, around 40 to 50 seconds. When the vehicle is changed, the “dirty” sprayer is then replaced with the “clean” sprayer standing by. In the same spirit, only the cover of the sprayer may be replaced when changing vehicles.
However, these solutions are not satisfactory, since they do not make it possible to obtain an optimal cleaning quality of the dirty painting equipment during application of the coating. Indeed, the component parts of the sprayers are parts with a complex geometry having many recesses, which makes them difficult to clean. Furthermore, all of these recesses form potential liquid solvent retention zones, which must be dried for a long time, since they may allow accumulated solvent residues to escape. Yet the time allocated to cleaning is too short to guarantee perfect drying of the rinsed surfaces.